SCIENCE
LESSON – 1 LIGHT
I. CHOOSE THE CORRECT ANSWER :1. Light travels only in a ______ .It is because of this property that.
(a) curved line, shadows
(b) straight line, shadows
(c) straight line, reflection
(d) curved line and then straight line, shadows
2.. Light that hits a mirror gets ______
(a) Transmitted
(b) Reflected
(c) Absorbed
(d) Refracted
3. ______ surface reflects the light well
(a) Water
(b) Compact disc
(c) Mirror
(d) Stone
4. Light is a form of ____
(a) matter
(b) energy
(c) medium
(d) partical
5. You can see your image in polished floors, but not in wooden table
because ______
(a) regular reflection takes place in wooden table and irregular reflection in
polished floor
(b) regular reflection takes place in polished floor and irregular reflection in
wooden table
(c) regular reflection takes place in both polished floor and wooden table
(d) irregular reflection takes place in both polished floor and wooden table
6. Choose the translucent substance from the following
(a) glass
(b) wood
(c) water
(d) Clouds
7. Reflection occurs , when the light
(a) about to reach a surface
(b) approaches a surface
(c) passes through a surface
(d) None Of these
8. Which of the following is the best reflector
(a) plastic plate
(b) plane mirror
(c) wall
(d) paper
9. Sivarajan placed a meter stick in the playground at 7.00 am in the
morning. How will the shadow of the stick at noon look in comparison to
the one in the morning
(a) There will be no shadow
(b) The shadow will be longer and on the opposite side as the sun
(c) The shadow will be shorter and on the same side as the sun
(d) The shadow will be shorter
10. The image formed by a pinhole camera is inverted because,
(a) light travels in straight lines
(b) light rays become laterally inverted as they pass through a pinhole
camera
(c) light rays pass through the pinhole
(d) light rays get reflected
11.Which of the following facts explain how shadows are formed?
(a) Light travels in straight lines
(b) Opaque bodies do not allow light to pass through them
(c) Reflection occurs at a smooth surfaces like mirrors
(d) Lateral inversion happens
(a) both A and B
(b) both A and D
(c) both B and C
(d) only A
II . FILL IN THE BLANKS :1.
2.
3.
4.
5.
6.
7.
8.
A plane mirror produces virtual and erect a image
A regular reflection helps us to see the objects.
The light ray gets reflected when it falls on any polisher surface
Sunlight is a blend of seven colours
The splitting of white light into seven colours is called dispersion
The moon reflects sun light.
The sunlight can be split into its constituent colours using prism
Reflection of light from rough surface is called irregular reflection
III . TRUE OR FALSE , IF FALSE GIVE THE CORRECT STATEMENT
1.The image of right hand in a plane mirror looks like a left hand.
TRUE
2.Rainbow is formed by dispersion of which light by water drops.
TRUE
3.The image formed by the plane mirror is laterally inverted, hence the
image seen through the periscope is also laterally inverted
FALSE
Correct Statement : The image formed by the plane mirror is laterally
inverted, hence the image seen through the periscope is This is because in
periscope, image is reflected by two mirrors.
4.We see planets because they reflect light from the sun
TRUE
5.We see a book because it reflects the light that falls on its surface
TRUE
6.The image formed in a pinhole camera is always inverted
TRUE
7. The image formed in a pinhole camera is always the same size as the
object
FALSE
Correct Statement: The image formed in a pinhole camera is always the
different size as the object
8.The image formed in a plane mirror is upside down
FALSE
Correct Statement : The image formed in a plane mirror is erect
9.A plane mirror is opaque
TRUE
10.A shadow is formed on the same side of the object as the source of
light.
FALSE
Correct Statement : a shadow is formed on the different side of the object
as the source of light
11. We are able to see things around us with the help of regular reflection
Answer:
TRUE
12. After passing through a prism, white light splits into a band of seven
colours
TRUE
IV . MATCH THE FOLLOWING
1. Rectilinear propagation
-
Pinhole camera
2. Plane Mirror
-
Periscope
3.
Fire fly
-
luminous object
4. The Moon
-
Non-luminous object
5. Wide light source
-
Penumbra
6.
Regular reflection
-
7.
The sun
-
Primary source of light
8.
Band of seven colours
-
Spectrum of light
Glossy surface
V . ANSWER THE FOLLOWING QUESTION IN SHORT :1.With the help of a diagram, state the laws of reflection
Answer:
Laws of reflection:
1. The angle of incidence is always equal to the angle of reflection li =l*
2. The incident ray, the reflected ray and the normal at the point of
incidence lie on the same plane
2.Figure shows a pencil placed above a mirror
a)Draw its image formed by the mirror
b) Show how light rays from the object are reflected at the mirror to form
the image for the eye.
3.A person is looking at the image of a tree in a mirror placed 3.5 m in front
of him. Given that the tree is at 0.5 m behind his eyes. Find the distance
between the image of the tree and his eyes. What are needed to see an
object?
Distance between the person and the mirror = 3.5 m
Distance between the person and tree (object) = 0.5 m
The image formed in the mirror = 4 m
The distance between the image of the tree and his eyes = 4 + 3.5 = 7.5
4. What are luminous objects?
All objects which emit light energy by themselves are called luminous
objects. Ex.: Sun, electric bulb.
5. Is the moon a luminous object?
No, the moon is non-luminous. The reason is that moon does not
produce its own light. Instead, it reflects the light of the sun falling on
it.
6. What are the three types of materials based on the absorption of light?
Answer:
1. Transparent Material
2. Translucent Material
3. Opaque Material
7.What are the parts of shadow?
1. Umbra
2. Penumbra
8.What are the properties of shadow?
Properties of shadow:
1. All objects do not form shadows. Only opaque objects form shadows.
2. Shadows will be formed in the opposite side of light source.
3. It cannot be determined the characteristics of an object by its
shadow.
4. The shadow will be always darker, whatever may be the color of light
rays.
9. What is plane mirror?
A plane mirror is a mirror with a flat reflective surface. A plane mirror
makes an image of objects in front of it.
10. What is prism?
Answer:
A prism is an object made up of a transparent material, like glass or
plastic that has at least two flat surfaces that form an acute angle
(less than 90°).
11. What do you mean by visible light?
Answer:
Visible light is a spectrum of a number of waves with different
wavelength range from 400nm to 700nm (lnm = 10″9 meter) each
wave has a definite wavelength represents a particular colour.
12. Write the items given here in the correct column (Stars, brick walls,
plants, mirror, planets, electric light bulb, candle)
Answer
Sources of Light
Objects that reflect light
Stars
Brick walls
Electric light bulb
Plants
Candle
Mirror
Planets
13. A boy of height lm 45 cm is standing in front of a long mirror at a
distance of 2 m. From this information, fill up the following sentences:
a) The distance between the boy and his image is ______
b) The height of the image is ______
c) When the boy moves 1 m forward, the distance between her and her
image is ______
Answer:
(a) The distance between the boy and his image is 4m
(b) The height of the image is same.
(c) When the boy moves 1 m forward, the distance between her and her
image is 2m.
Question 14.
Draw a diagram of a pinhole camera showing the rays of light passing
between the Object and its image
Answer:
Question 15.
Why is the writing on the front of an ambulance back to front as shown in
the picture
Answer:
1. This is due to lateral inversion.
2. The phenomenon due to which the left side of an object appears to
be right side of the object in its image in a reflecting medium
(mirror).
3. So that drivers see the word the right way around in their rear-view
mirror.
Question 16.
Explain with examples, why some capital letters look the same in a mirror
but others are reversed.
Answer:
Any letter that has a bilateral symmetry will have its mirror image the same
as that of the object.
Example:
Question 17.
Two plane mirrors M1 and M2 are placed perpendicular with each other, as
shown in figure. The ray AB makes an angle 39° with the plane mirror M ,
then
1.
2.
3.
4.
The reflected rays are _________, ____________
The incident rays are _________, ____________
What is the angle of incident corresponding to the ray BC?
What is the angle of reflection corresponding to the ray CD
Answer:
1.
2.
3.
4.
BC, CD
AB, BC
⌊ i = 39°
⌊ r = 39°
Question 18.
Raj an was playing with the mirror images of a clock. He looked at the clock
in his roomIt was showing 1:40. Draw the position of the hands on the real
clock and on its mirror reflection .Write below the picture what time each
picture
Answer:
Question 19.
What is reflection of light?
Answer:
The bouncing back of light from a reflecting surface of an object is called as
reflection of light
Question 20.
If a ray of light is falling on a plane mirror at an angle of 50° is formed, what
will be the angle of reflection?
Answer:
Angle of incidence ⌊ i = 90° – 50°
⌊ i = 40°
According to laws of reflection,
⌊i=⌊k
Angle of incidence = Angle of reflection
⌊ i = 40°
∴ ⌊ r – 40°
Angle of reflection ⌊ r = 40°
Question 21.
What do you mean by lateral inversion?
Answer:
The phenomenon due to which left hand side of object appears as right
hand side and vice versa is called lateral inversion.
Question 22.
How do you obtain a spectrum of light?
Answer:
When white light is made to fall on the surface of a prism, it disperses and
we obtain a spectrum of light.
Question 23.
Why do we see white color in Newton’s disc, when we rotate it very fast?
Answer:
When the disc turned quickly, the retina receives the sensation of the
spectrum simultaneously and disc appears white.
Question 24
What is a shadow? What things are necessary for the formation of a
shadow?
Answer:
1. Shadows are formed because light travels in straight lines.
2. Shadow is always against, opposite side of light source.
3. Shadow is formed by opaque objects that stop high from
propagating.
4. Things necessary for the formation of shadow: source of light,opaque
object
VI. ANSWER IN DETAIL
Question 1.
What are regular and irregular reflection? Explain with the help of diagrams
Answer:
(i) Regular reflection When a parallel beam of light on striking some
smooth and polished surface is reflected as a parallel beam of light, such a
reflection is called regular reflection.
(ii) Irregular reflection : When a parallel beam of light, on striking some
rough surface, is reflected in different directions, then such a reflection is
called irregular or diffused reflection.
Question 2.
What are the difference between luminous and non-luminous objects? Give
two examples of each.
Answer:
Luminous objects
1.
2.
All objects which emit light energy by themselves are
called luminous objects.
Ex.: Sun, stars, torch light, burning candle etc.
Non-luminous objects
All objects which do not emit light ene
own, but reflect the light energy falling
hence, become visible are called non- l
object.
Ex.: Metals, trees, houses, stones, moo
Question 3.
Write about two everyday situations that tell you that light travels in a
straight line.
Answer:
1. Formation of shadow: Shadows are formed when some light rays
continue its travel in straight lines while other rays are stopped by an
object.
2. When there is a small hole in a room, light travels only in a straight
line.
Question 4.
Differentiate between a reflection and a shadow
Answer:
Reflection
Shadow
When light falls on a surface, the direction of ray
is changed. This change in direction is known as Shadow is an image formed by obstruction of light.
reflection of light.
Eg.: If you place your hand in front of a candle, you will s
Eg.: You see your reflection in a pool of water or
of the hand on the wall. This image will show only the out
mirror.
object placed in front of the light source.
Question 5.
What are the characteristics of an image formed in a plane mirror?
Answer:
1. Image formed in a plane mirror is upright.
2. Image formed in a plane mirror is virtual The image is of the same
size as the object
3. The distance of the image from the plane mirror is equal to the
distance of the object from the mirror.
4. Image is laterally inverted.
Question 6.
Describe the picture
Answer:
1. When the tube is bent, we cannot see the source of light
2. When the tube is held straight we can see the flame. The two pictures
verify that light travels in straight lines. This is known as rectilinear
propagation of light.
Question 7.
Define the following terms
a. Incident ray
b. Reflected ray
c. Normal
d. Angle of incidence
Answer:
(a) Incident tavi The ray of light that falls on the surface of the reflection
materials.
(b) Reflected ray: The ray of light that comes from the point when the
incident ray falls on the reflection material.
(c) Normal: The perpendicular line drawn from, the point of incidence to the
plane of reflecting surface is called normal.
(d) Angl e of incidence The angle formed between the incident ray PO and
the normal ‘ON’ is angle of incidence.
Question 8.
Compare the images formed by plane mirror with that by pinhole camera
Answer:
Difference between the images formed in Pinhole camera and Plane mirror:
Image formed by Pin hole camera
The image is real.
The image may not be equal to the size of the object
The image is inverted
Images formed in Plane mirror
The image is virtual
The image is equal to the size of the object
The image is erect